As is known, a motor vehicle comprises an internal combustion engine comprising a plurality of cylinders. Each cylinder is connected to a piston and comprises a combustion chamber, into which an injector introduces fuel, of which the combustion combined with a combustion agent allows the actuation of the piston. The mechanical force created by the movement of the piston is then transmitted, via transmission elements, to the wheels of the vehicle in order to set said vehicle in motion.
Some fuels, such as ethanol for example, require heating in order to keep them at a minimal temperature of approximately 27° C. in the case of ethanol, because otherwise the combustion of these fuels may be slowed or even inhibited.
To this end, it is known to use a heating module comprising a plurality of induction coils, each coil being mounted around an injector so as to provide said injector with heat when the coil is excited by a current, which then makes it possible to raise the temperature of the fuel passing through the injector.
A device for controlling the heating module makes it possible to control the supply of current to the coils and therefore the heating temperature of the fuel passing through the injectors. Such a device, as is known, comprises a phase shift unit and a battery generating an electric supply current. The phase shift unit comprises a plurality of H bridges connected to said battery and a means for controlling the phase shift of the H bridges relative to one another. The number of H bridges is equal to the number of induction coils, and each H bridge delivers, from the electric supply current provided by the battery, an electric excitation current at the associated induction coil of said H bridge. The battery delivers a continuous current transformed into alternating current of sufficiently high amplitude and frequency to quickly heat the coils, for example 25 amps at 10 kHz.
Each H bridge performs the function of providing to the associated coil an alternating current of which the half-period is defined by a duty cycle. Thus, for example, when the duty cycle is n %, a current of positive amplitude is delivered during n % of the time of a half-period, then the delivered current is zero during the (100−n) % of the remaining time of said half-period. During the following half-period, a current of negative amplitude, which is equal in terms of absolute value to the value of the current of positive amplitude delivered at the previous half-period, is delivered during n % of the time of a half-period, then the current delivered is zero during the (100−n) % of the remaining time of said half-period.
Since the heating power provided by a coil is dependent on the amount of current received continuously, the duty cycle of the current provided by each H bridge is adjusted between 0% and 100%, such that the associated coil provides the desired heating power.
Since the current provided by the battery is dependent on the number of H bridges functioning simultaneously, the phase shift unit is configured to phase shift the operation of the H bridges, for example by 45°, such that said bridges supply the coils in a manner offset over time. In other words, some H bridges deliver current simultaneously, but not all the H bridges deliver current simultaneously. In fact, a simultaneous provision of current by the set of H bridges would lead to an excessive consumption of the battery and to very severe variations in the amplitude of the current of said battery.
Although the current signals delivered by the H bridges phase shifted in this way reduce the variations in amplitude of the current of the battery to a certain extent, they are still just as high and for example may reach several tens of amps.
Such undulations of the current delivered by the battery of the control device may induce electromagnetic waves, which may influence the operation of the electronic components and equipment arranged in the vicinity and thus constitute a significant disadvantage.
In order to overcome this disadvantage, it is known to use a filter referred to as an “EMC” (electromagnetic compatibility) filter, which prevents the significant undulations of the current delivered by the battery.
Such a filter, however, requires the use of one or more capacitors of very high value in the order of 3 000 μF in order to absorb the undulations of the current. The dimensions of such capacitors are relatively substantial, in the order of several centimeters, which considerably increases the size of the device and constitutes a significant disadvantage, in particular within the scope of the use of said device in a motor vehicle in which the available space is limited. Such capacitors also constitute a further cost.